Key immunologic and clinical safety issues will be directly evaluated in concert with in vitro analysis of human T cell clones and in vivo studies in a murine model. In the first phase (R21) of this application, milestones for APL specificity, sensitivity, and activity on polyclonal T cells will be addressed by both structural and mechanistic approaches. Antigenic cross-reactivity with native hGAD65 will be rigorously evaluated in HLA-DR4 transgenic mice to meet milestones for advancing to the second phase (R33) of this project. After successful completion of these milestones, we propose to submit an IND and clinical trial protocol for a phase I study in patients. Safety criteria for this phase of the application include immunologic, metabolic, and neurologic outcomes. Novel HLA-GAD tetramer assays will be used to evaluate immunologic perturbations of antigen-specific CD4+ T cells during therapeutic APL administration. This research plan combines the expertise of Dr. G. Nepom's immunology laboratory with the clinical research expertise of Dr. C. Greenbaum in a collaborative partnership for comprehensive evaluation of a potential new diabetes therapy. This team of basic and clinical scientists at VMRC holds joint weekly meetings and is well suited to expeditiously move from feasibility studies to development and clinical trials.